New methods have been reported in the scientific literature for the direct conversion of alkylaromatic compounds to esters.
Journal of Organic Chemistry, 34 (No. 4), 1106 (1969) describes a palladium-catalyzed conversion of xylene to xylyl acetate, p-xylylene diacetate and p-methylbenzylidene diacetate. The xylene oxidation is conducted in acetic acid, employing a palladium-stannous acetate catalyst and air.
Oxidation Communications, 7 (Nos. 1-2), 69 (1984) cribes the kinetics of toluene oxidation to benzyl acetate in the presence of Pd(OAc).sub.2, Sn(OAc).sub.2 and KOAc. The active catalytic species is a heterogeneous combination of palladium, tin and oxygen.
Of related interest with respect to the present invention are U.S. Pat. Nos. 4,317,460; 4,524,051; and 4,855,274. These references disclose palladium-tin and other catalysts for the oxidation of carbon monoxide to carbon dioxide.
There is continuing interest in the development of stable catalyst systems for oxidation of organic compounds with high selectivity and efficiency.
Accordingly, it is an object of this invention to provide an improved palladium-tin catalyst for selective oxidation of organic compounds.
It is a further object of this invention to provide a process for acyloxylation of a C.sub.1 -C.sub.4 alkyl-substituted aromatic compound to an alpha-acyloxy C.sub.1 -C.sub.4 alkyl-substituted aromatic compound, with a palladium-tin catalyst exhibiting high oxidation efficiency and a stable oxidation rate.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.